1. Field of the Invention
The present invention generally relates to liquid-crystal-display devices, and particularly relates to a liquid-crystal-display device that is of a type having peripheral circuits integrated therein, and is capable of displaying a large and fine screen.
2. Description of the Related Art
In recent years, there has been a demand for a large-scale fine display as well as for a small-scale fine display. Such a demand has led to an increase in popularity of liquid-crystal-display devices using p-SiTFTs (poly-silicon thin film transistors), which allows the liquid-crystal display unit and peripheral circuits to be formed as an integrated device.
One type of liquid-crystal-display devices, which is relevant to the present invention, has a liquid-crystal-display area thereof divided into a plurality of blocks, and a video signal is written into the blocks one block after another. Hereinafter, such a driving method is referred to as a simple-block-succession method.
FIG. 1 is a block diagram of a liquid-crystal-display device 10 which is an example of a liquid-crystal-display device driven by the simple-block-succession method.
As shown in FIG. 1, the liquid-crystal-display device 10 includes a digital driver LSI 12, common-signal lines D1 through Dn, analog switches 14, block-control lines BL, a gate driver 16, and a display matrix 18. The digital driver LSI 12, the common-signal lines D1 through Dn, the analog switches 14, etc., together form a data driver 19.
The display matrix 18 is divided into N blocks B1 through BN, and each block is provided with scan lines 20 and signal lines 22 arranged in a matrix form. At intersections of the scan lines 20 and the signal lines 22 are situated pixel cells 24.
The analog switches 14 include as many as n switches provided for each of the blocks B1 through BN. The analog switches 14 are connected to the common-signal lines D1 through Dn via lead lines 31. Each of the analog switches 14 is also connected to the block-control lines BL. The analog switches 14 are turned on when block-control signals BL1 through BLN are supplied through the block-control lines BL.
The digital driver LSI 12 receives digital signals from an external data-supply device (not shown), and generates video signals Vs based on the received digital signal. The digital driver LSI 12 supplies the video signals Vs to each of the blocks B1 through BN via the common-signal lines D1 through Dn on a time-division basis.
When the liquid-crystal-display device 10 operates, a scan signal Vg supplied from the gate driver 16 activates successively the pixel cells 24 one line after another. In the liquid-crystal-display device 10, a horizontal scan period Th is comprised of N block-control periods Tb. During the first block-control period Tb, the block-control signal BL1 turns on n analog switches 14 that are connected to the signal lines 22 within the block B1. During the second block-control period Tb, the block-control signal BL2 turns on n analog switches 14 that are connected to the signal lines 22 inside the block B2. Further, during the N-th block-control period Tb that is the last in one horizontal scan period Th, n analog switches 14 connected to the signal lines 22 in the block BN are turned on by the block-control-signal BLN. Video signals Vs generated by the digital driver LSI 12 are supplied through the turned-on analog switches 14 to the activated pixel cells 24, thereby effecting liquid-crystal display.
FIG. 2 is a block diagram for explaining configurations of the data driver 19 and the display matrix 18 provided in the liquid-crystal-display device 10. FIG. 2 shows a configuration of n being 384 and N being 10 in the configuration of FIG. 1. Namely, the display matrix 18 is divided into 10 blocks, and the number of horizontal pixels is 3840 (=384xc3x9710).
As shown in FIG. 2, the data driver 19 includes the digital driver LSI 12, the common-signal lines D1 through D384, the analog switches 14, etc. The digital driver LSI 12 has 384-bit outputs, which correspond to the common-signal lines D1 through D384. The analog switches 14 are provided as many as 384 for each of the blocks B1 through B10. The common-signal lines D1 through D384 are connected to a corresponding one of the analog switches 14 in each of the blocks B1 through B10.
In general, one horizontal scan period Th becomes shorter as size of the liquid-crystal-display area increases. In the VGA format having 640xc3x973(RGB)xc3x97480 pixels, the horizontal scan period Th is approximately 34.6 xcexcs whereas in the QXGA format having 2048xc3x973xc3x971536 pixels, the horizontal scan period Th is approximately 10.8 xcexcs.
In the liquid-crystal-display device 10 described above, a time period required for writing signals in one block, i.e., the block-control period Tb, is determined by 1 horizontal scan period Th/the number of blocks N. As the horizontal scan period Th decreases with an increase in size of the display area, the block-control periods Tb also decreases.
In order to maintain a sufficient block-control periods Tb, width of each block may be widened, and the number N of the blocks may be decreased. When this measure is taken, however, the problem as follows will be encountered.
As shown in FIG. 1, the liquid-crystal-display device 10 has a data width (number of bits) of one block being equal to the number n of the common-signal lines D1 through Dn. When the data width is increased, the number of the common-signal lines is also increased, resulting in an increase in space required for the wiring of the signal lines. This makes larger the frame size of the display panel of the liquid-crystal-display device 10.
For example, when an XGA panel having 3072 horizontal pixels and a 22-microsecond horizontal scan period Th is implemented by using 8 blocks having the data width of 384 bits, the block-control periods Tb will be longer than 2.0 xcexcs. In order to achieve a 2.0-microsecond block-control periods Tb by using a QXGA panel having 6144 horizontal pixels and an 11-microsecond horizontal scan period Th, 4 blocks each having a data width of 1536 bits must be used. In this case, assuming that the wiring pitch is 16 xcexcm, the wiring width of the common-signal lines D1 to D384 in the XGA panel is 6.14 mm (16 xcexcmxc3x97384 bits). In contrast, the wiring width of the common-signal lines D1 to D1536 of the QXGA panel is 24.6 mm (16 xcexcmxc3x971536 bits). This is quite a wide width.
Further, when the digital driver LSI 12 is used as an external attachment to the liquid-crystal-display device 10, an increase in the width of the common-signal lines D1 through Dn results in an increase in the number of outputs of the digital driver LSI 12. Consequently, the digital driver LSI 12 becomes highly expensive, and the yield in the manufacturing process decreases.
Moreover, widening the data width leads to an increase in the number of intersections of the common-signal lines D1 through Dn and the lead lines 31 shown in FIG. 1, resulting in the capacitance load on the common-signal lines D1 through Dn being increased. This means an increased time constant. In the QXGA panel, for example, a single common-signal line may have more than 6144 intersections. In such a case, the capacitance load of one intersection point may be 4 fF, for example, and, then, the total capacitance may be as large as 25 pF.
As shown in FIG. 1, the liquid-crystal-display device 10 has the common-signal lines D1 through Dn the length approximately equal to the width of the display matrix 18. As the size of the display matrix 18 is increased, therefore, the length of the common-signal lines D1 through Dn is also increased. The resulting increase in the wiring resistance contributes to a rise in the time constant.
Accordingly, there is a need for a liquid-crystal-display device which can provide high image quality, yet is small in size and provided at low cost.
It is a general object of the present invention to provide a liquid-crystal-display device that substantially obviates one or more of the problems caused by the limitations and disadvantages of the related art.
Features and advantages of the present invention will be set forth in the description which follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by the liquid-crystal-display device particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a liquid-crystal-display device which displays an image on display matrix by supplying video signals to pixel cells of the display matrix, the liquid-crystal-display device including a data driver supplying the video signals to the display matrix and including N digital drivers, Nxc3x97k common-signal lines, and Nxc3x97kxc3x97n switch blocks, wherein every k lines of the Nxc3x97k common-signal lines are connected to a corresponding one of the N digital drivers, and every n blocks of the Nxc3x97kxc3x97n switch blocks are connected to a corresponding one of the Nxc3x97k common-signal lines, each of the common-signal lines being comprised of m lines and each of the switch blocks includes m selection switches, which couples the common-signal lines to the pixel cells of the display matrix.
In the liquid-crystal-display device described above, each digital driver has k common-signal lines connected thereto, so that the number m of signal lines that constitute any given one of the common-signal lines can be 1/k of that of the related-art configuration. This makes it possible to make the wiring width of the common-signal lines 1/k as wide as the related art. As a result, the size of panel frames can be reduced.
Further, since the number m of the signal lines in each of the common-signal lines is 1/k of that of the related art, the common-signal lines intersect with lead lines at 1/k as many locations as in the related art where the lead lines connect between the common-signal lines and the selection switches. This reduces intersection capacitance of the common-signal lines.
Further, the present invention allows digital drivers having a relatively small number of outputs to be used, which leads to a cost reduction of the digital drivers.
According to another aspect of the present invention, the liquid-crystal-display device as described above is such that one horizontal scan period includes n timing periods, during each of which one of the every n blocks of the Nxc3x97kxc3x97n switch blocks is selected by a control signal, the digital drivers supplying the video signals to the pixel cells that are connected by the selection switches of the selected switch blocks.
In the liquid-crystal-display device described above, switch blocks are selected one each for a corresponding one of the common-signal lines during each timing period, which makes it possible to write video signals as data having a wide data width without increasing the wiring width of the common-signal lines and without increasing the capacitance load and the resistance load.
According to another aspect of the present invention, the liquid-crystal-display device as described above is such that the data driver includes first through third layers, the digital drivers being arranged in line in the first layer, the common-signal lines being arranged in line in the second layer, and the switch blocks being arranged in line in the third layer.
When the common-signal lines having 1/k of the horizontal extension of the related art are arranged in one line, the wiring resistance of each common-signal line becomes 1/k as small. In the liquid-crystal-display device of the present invention, reductions in the intersection capacitance and the wiring resistance result in a significant decrease in the RC time constant. Therefore, the present invention can improve image quality by the improved time constant.
Further, if the digital drivers are implemented as a panel-built-in circuit based on p-SiTFT that helps to reduce circuit size, a reduction of power consumption can be achieved. Since the number of TFTs constituting the digital drivers can also be reduced, a yield of the manufacturing process is also improved. Further, the present invention can widen the pitch of output terminals of the digital drivers.